This invention relates to a quartz crystal oscillator circuit, and particularly to an oscillator circuit for use in an electronic wrist watch and which includes a flexural quartz crystal vibrator of the tuning fork type.
Modern electronic wrist watches employ oscillator circuits which includes a quartz crystal vibrator as a frequency standard. In particular, these electronic wrist watches use flexural quartz crystal vibrators of the tuning fork type, and as a result it is possible to realize a highly accurate wrist watch. Because of this high accuracy time correction is very infrequently required so that it is greatly desired that such wrist watches have a long battery life in order to provide a wrist watch requiring substantially no servicing for very long periods of time.
Generally, a quartz crystal vibrator of the tuning fork type is designed so that the electromechanical coupling factor k thereof is maximized. The electromechanical coupling factor of a conventional flexural quartz crystal vibrator of the tuning fork type is about 4% at maximum efficiency. If one tries to obtain a stable frequency in an oscillator circuit using a quartz crystal vibrator of the tuning fork type having a high electro-mechanical coupling factor k of about 4%, the resultant electrical current consumption of the circuit will be high because the high electromechanical coupling factor k of the quartz crystal vibrator requires a large load capacitance to insure frequency stability. Therefore, in the conventional oscillator circuit it is impossible to have both long battery life and high frequency stability in an electronic wrist watch.